Dust seal for electric motors

ABSTRACT

A dust seal structure applied to electric motors to prevent ingress of dust and other foreign matter into the air gap between the stator and rotor includes a stator supported ring-shaped lip seal member and a ring-shaped spacer member which bear in an axial direction against a corresponding surface on the rotor. The lip seal and spacer members are mounted on an axially movable support ring which is carried by the radially inner ends of a circumferential array of flexible strips whose outer ends are secured to the stator, and compression springs associated with the flexible strips exert an axially directed force which is transmitted to the lip seal and spacer members thus to enable the latter to follow any axial movements of the rotor. The spacer member which is non-yieldable absorbs axial thrust exerted by the springs and thus prevents the lip seal from being deformed as well as acting as a guide for the seal.

United States Patent Rutz et al. 5] June 27, 1972 1 DUST SEAL FORELECTRIC MOTORS 2,522,231 9/1950 Loftis ..277/95 x [72] Inventors:Hansrudolf Rutz, Wettingen; Tassilo Schmollinger, Gebenstorf, both ofSwitzer- Pnmary mgr-'1) slmey land AttorneyPierce,.Schefiler & Parker[73] Assignee: Aktiengesellschaft Brown, Boveri & Cie, [57] ABSTRACTBaden, Switzerland A dust seal structure applied to electric motors toprevent in- [22] Filed: Dec. 21, 1970 gress of dust andother foreignmatter into the air gap between the stator and rotor includes a statorsupported ring-shaped lip [211 App]' 99836 seal member and a ring-shapedspacer member which bear in an axial direction against a correspondingsurface on the re- [30] Foreign Application Priority Data tor. The lipseal and spacer members are mounted on an axially movable support ringwhich is carried by the radially inner Jan. 7, 1970 Switzerland ..95/70ends of a circumferential array of flexible Strips whose outer ends aresecured to the stator, and compression springs as- F Z 62 sociated withthe flexible strips exert an axially directed force 58] d 277/95 whichis transmitted to the lip seal and spacer members thus to e o c enablethe latter to follow any axial movements of the rotor. The spacer memberwhich is non-yieldable absorbs axial [56] Reerenm Cited thrust exertedby the springs and thus prevents the lip seal UNITED STATES PATENTS frombeing deformed as well as acting as a guide for the seal.

1,750,818 3/1930 Sauveur ..3 10/88 X I 4 Claims, 3 Drawing Figures DUSTSEAL FQR ELECTRIC MOTORS seals between the stator and rotor of largeelectrical machines to prevent the ingress of dust, dirt and foreignmatter into the air gap between the stator and rotor. The knownconstructions of seals generally have a lip seal which covers the gapbetween the stator and rotor. It has also been proposed to constructsuch lip seals in adjustable form to enable a certain degree ofunavoidable wear to be compensated.

The known systems, however, suffer from various disadvantages, forexample when fitted into a cement grinding motor, exposed to largeconcentrations of dust. To minimize deflection of the radial ring sealsdue to the large thermal expansions and deformations which occur duringoperation, the clearance, normally amounting to 0.5 to 1 mm, would haveto amount to several millimeters. Tolerance of such magnitude wouldresult in the discharge of a substantial amount of cooling air which isrequired for the motor. Since the air pressure which prevails in theinterior of the machine is relatively high, this would necessitate theprovision of a large air leakage fan.

When the machine is shut down, this system of seals could allowuncontrollably large quantities of cement dust to penetrate into themotor. It is the object of this invention to avoid the disadvantages ofthe prior art. Since the sealing parts must be in physical contact witheach other in order to provide reliable sealing, 'it is necessary forthe individual sealing parts to be disposed movably in order to permitadaptation to the large relative movements. This is best accomplished byusing axially slidable ring seals.

The aforementioned problem is solved according to the present inventionin that the seals are constructed in a plurality of parts in order tocompensate for axial and radial movements of the rotor. One of the partsis a yieldable ring-shaped lip seal which bears axially against acorrespondingly positioned surface on the rotor while the other part,also ringshaped, but non-yieldableand bearing against the surface of therotor serves to absorb axial thrusts of the rotor and guide the lip sealas well as prevent deformation of the lip seal.

More particularly, the seal structure which prevents ingress of dust andother foreign matter into the air gap between the stator and rotorcomponents of the motor-"includes a stator supported ring-shaped. lipsealmember and a ring-shaped spacer member which bear in an axialdirection against a corresponding surface portion of the rotor. The lipseal and spacer members are mounted on an axially movable support ringwhich is carried by the radially inner ends of a circumferential arrayof flexible strips whose outer ends are secured to the stator, andcompression springs individual to each of the flexible strips exert anaxially directed force which is transmitted to the lip seal and spacermembers thus to enable the latter to follow any axial movements of therotor. The spacer member being non-yieldable absorbs axial thrustexerted by the springs and thus prevents the lip seal from beingdeformed as well as acting as a guide for the seal.

The improved multi-part ring seal structure according to the inventionassures a 100 percent sealing effect over a very large diameter.

In addition to the multi-part dust seal provided for sealing duringoperation of the motor, the invention also provides a ring-shapedbellows associated with the ring-seal which provides a further sealingeffect to prevent ingress of dust into the gap between the stator androtor, particularly when the motor is shut down, i.e., is at standstill.

One suitable embodiment of the invention will now be described in detailand is illustrated in somewhat simplified form in the accompanyingdrawings wherein:

FIG. 1 illustrates a dust seal of the type already known in the art;

FIG. 2 is a vertical section through the improved seal structure inaccordance with the present invention; and

FIG. 3 is a sectional view taken along line A-A of FIG. 2.

With reference now to the drawings, and to FIG. 1 in particular, forpurposes of background information, there is illustrated a radialsealing system of the type as known to the prior art. Numeral 1designates the stator of the motor on which is mounted a radial seal 3to cover the gap between the stator and the rotor 2 to prevent ingressof dust and other foreign matter. When such a radial seal is used, forexample, in a cement mill in which the grinding drum assumes a greateror lesser angle in operation due to temperature changes and thereforeresults in a relatively large radial and axial movement of the sealingsurface on the rotor, it follows that complete sealing to preventingress of dust cannot be ensured.

In accordance with the invention, as depicted ,in FIGS. 2 and 3, themulti-part ring seal includes a yieldable ring-shaped lip seal 8 and atleast one non-yieldable ring-shaped spacer strip 7 (two concentric rings7 are shown) which bear in an axial direction against a correspondingsurface portion of the rotor 2. The lip seal 8 and the two spacermembers 7 disposed in concentric radial relation to the axis of therotor. are secured to an axially movable resiliently mounted supportring 6 which is carried by the inner ends of a circumferential array offlexible strips 9 whose outer ends are secured to the stator.Compression springs 5 individual to the flexible strips 9 exert anaxially directed force against the strips which, in turn, is transmittedthrough the support ring 6 to the lip seal 8 and spacer members 7 thusto enable the latter to follow any axial movement of the rotor withoutdisturbing the seal. The concentric, radially spaced, non-yieldablespacer members 7 absorb axial thrust exerted by the springs 5 as theypress against the shaft surface and thus prevent the lip seal 8 frombeing deformed, as well as acting as a guide for the lip seal.

A ring-shaped bellows 4 located radially inward of the flexible strips 9and their springs 5 functions to prevent ingress of dust and otherforeign matter into the gap between stator and rotor, particularly whenthe motor is shut down, i.e., is at standstill.

Thus, the ring-shaped seal assembly comprising the ring lip seal 8 andspacer ring members 7 which bears in a resilient manner against thesurface of the rotor effects the desired seal and which issatisfactorily maintained even though there be some radial and/or axialdisplacement of the rotor relative to the stator.

The inventive concept is not limited to the actual embodiment which hasbeen illustrated. It is possible, for example, to locate the lip seal 8radially inward of the ring spacers 7, or between the two ring spacers.

We claim:

1. In a dust seal structure applied in electric motors to preventingress of dust and other foreign matter into the air gap between thestator and rotor, the combination comprising a yieldable ring-shaped lipseal member and a non-yieldable ring-shaped spacer member which bear inan axial direction against a corresponding surface on the rotor, asupport ring on which said lip seal and spacer members are mounted,means for resiliently securing said support ring to said stator, andmeans including spring means for applying an axially directed forceagainst said support ring and which is correspondingly transmitted tosaid lip seal and spacer members thereby to enable the latter to followany axial movement of the rotor, said spacer member serving to absorbthe axial thrust applied to said support ring and thereby preventdeformation of said lip seal member.

2. A dust seal structure for electric motors as defined in claim 1wherein said means for resiliently securing said support ring to saidstator is constituted by a circular array of circumferentially spacedflexible strips and wherein said spring means for applying an axiallydirected force against said support ring is constituted by compressionsprings which respectively bear against said flexible strips.

3. A dust seal structure for electric motors as defined in claim 1 andwhich further includes a ring-shaped bellows secured to the stator andwhich prevents ingress of dust and other foreign matter into the gapbetween the stator and rotor and particularly when said motor is atstandstill.

4. In a dust seal structure applied to electric motors to preventingress of dust and other foreign matter into the air gap between thestator and rotor the combination comprising a ring-shaped yieldable lipseal member and a ring-shaped non-yieldable spacer member which bear inan axial direction against a corresponding surface on the rotor, saidlip seal and spacer members being mounted on an axially movable supportring carried by the radially inner ends of a circumferential array offlexible strips whose outer ends are secured to the sta-

1. In a dust seal structure applied in electric motors to preventingress of dust and other foreign matter into the air gap between thestator and rotor, the combination comprising a yieldable ring-shaped lipseal member and a non-yieldable ringshaped spacer member which bear inan axial direction against a corresponding surface on the rotor, asupport ring on which said lip seal and spacer members are mounted,means for resiliently securing said support ring to said stator, andmeans including spring means for applying an axially directed forceagainst said support ring and which is correspondingly transmitted tosaid lip seal and spacer members thereby to enable the latter to followany axial movement of the rotor, said spacer member serving to absorbthe axial thrust applied to said support ring and thereby preventdeformation of said lip seal member.
 2. A dust seal structure forelectric motors as defined in claim 1 wherein said means for resilientlysecuring said support ring to said stator is constituted by a circulararray of circumferentially spaced flexible strips and wherein saidspring means for applying an axially directed force against said supportring is constituted by compression springs which respectively bearagainst said flexible strips.
 3. A dust seal structure for electricmotors as defined in claim 1 and which further includes a ring-shapedbellows secured to the stator and which prevents ingress of dust andother foreign matter into the gap between the stator and rotor andparticularly when said motor is at standstill.
 4. In a dust sealstructure applied to electric motors to prevent ingress of dust andother foreign matter into the air gap between the stator and rotor thecombination comprising a ring-shaped yieldable lip seal member and aring-shaped non-yieldable spacer member which bear in an axial directionagainst a corresponding surface on the rotor, said lip seal and spacermembers being mounted on an axially movable support ring carried by theradially inner ends of a circumferential array of flexible strips whoseouter ends are secured to the stator, and compression springs associatedwith said flexible strips and which exert an axially directed forcetransmitted through said support ring to said ring-shaped lip seal andspacer members thus to enable the latter to follow any axial movement ofthe rotor, said spacer member serving to absorb the axial thrust exertedby said springs thereby to prevent deformation of said lip seal member.